This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. A. SPECIFIC AIMS The primary objective of this clinical study is to determine the impact of inhaled MJ smoke and THC on human immune responses to an antigen challenge and the potential for MJ use to increase the risk for serious viral infections as measured by the immune response to Hepatitis B vaccination. The following specific outcomes will be determined: " HBsAb titer by ELISA assay. " HBsAg-specific T cell proliferation " Frequency of HBsAg-specific T cells and the distribution of the following subsets as determined by flow cytometry analysis: CD4/CD8 responders, Th1/Th2/Treg cells, and na[unreadable]ve versus memory T cells.